1. FIELD OF THE INVENTION
This invention pertains generally to interfaces between humans and tools, and more specifically to tactile input devices which signal both an intention and a direction of control from the human to the tool. The tool may include a large motorized vehicle or a tiny micromanipulator, and will include many other devices, both large and small.
2. DESCRIPTION OF THE RELATED ART
The ways in which humans interact with the tools of mankind has been studied and improved upon since the beginnings of man. With each improvement, in either the tool or the method of interaction, some benefit comes. The benefit may be in greater output per unit of time or in greater power or influence. In either case, the motivation has been sufficiently great to cause a continued evaluation of both the tool and the interface between humans and the tool.
With the great progress made recently in the field of electronics, electrical and electronic controls are a part of most modern tools. These tools may take the form of automobiles, computers, appliances, toys, laboratory equipment, and other diverse machines and devices. Some of these controls may have some intelligence in the form of a computer microchip and a computer program. Other controls require direct input from an operator and respond only thereto, such as large servo systems. The electrical or electronic controls will typically monitor some type of actuator for a signal or specific input from the human operator, and the control system will generate an electrical output which will in some way control another device. Often times there is a need for determining one or several factors which include an intention on the part of the operator to provide input, an indication of the magnitude of the input, and also an indication of a direction of intent.
The devices used to provide input from the human are as varied as the equipment which is controlled. Any parameter which is generally known to be measurable electrically has been used as the basis for an input device. Resistive, capacitive, inductive, magnetic, and piezoelectric devices have all been devised to monitor for input from a human to the device, and to convert the input to an electrical signal which may then be relayed on to other electrical devices.
Among the relatively recent innovations are computer mice, trackballs, force sensitive resistors, strain gauges, and digitizing tablets. Each of these devices convert one form of input or another from a human to an electrical signal which may be monitored by associated electronics. However, these devices are restricted in a number of undesirable ways. For example, the computer mouse requires significant free surface area for manipulating the rolling ball. Additionally, mice are prone to making poor contact either between the typical ball and rollers or between the ball and surface, leading to poor control. Trackballs require rapid hand motions together with great dexterity. Precision is usually sacrificed, though trackballs offer the advantage of being self-contained, thereby resolving some of the disadvantages of computer mice. Digitizing tablets are typically quite large to gain any resolution, and in addition are typically quite complex and expensive. Capacitive, inductive and other tactile sensors, voice actuators and other various input devices tend to be more complicated electronically, and are often more susceptible to damage, environment and external electromagnetic interference.
Force sensitive resistors in one form or another have recently offered much promise through a combination of smaller sizes, lower costs and enhanced reliability and performance. This is all achieved through a variety of designs incorporating a variety of resistor materials from strain gauge resistors whose resistance changes in accord with a gauge factor to compressible resistor materials whose resistance is dependent upon the degree of compression, to contactor type variable resistors where either a sliding contactor or a flexible film may be brought into contact with a resistor material to induce a voltage output.
The present invention is of this last category, utilizing a flexible film as a contact material. U.S. Pat. No. 4,444,998, incorporated herein by reference in entirety, is most exemplary of this technology. Therein, one or more flexible resistive films are arranged in planes parallel to a conductive planar member. Pressure applied to the flexible films causes electrical contact to occur with the conductive planar member. Intent to control the device is thereby established, and, based upon the position of the contact, which in the disclosed embodiment may be anywhere within the two axes of the plane, a direction and magnitude may be determined by the electronics. This prior art interface device offers simplicity in manufacture and significant resistance to environment and external electromagnetic interference. However, the device does not offer small size and precision together in one device. The size of the human operator's finger relative to the pad must be small for any sensitivity and precision. If the finger is large relative to the device, just deflection of the finger as force is applied leads to a change in output. A light touch will read differently than a hard touch. Further, the zero or center point is difficult to control, and will be affected by the geometry of the finger and the consistency of the resistor film.
There is a need in the industry for a very small and relatively low cost device which will provide a reliable indication of intent, direction and magnitude. Such a device will have wide and diverse industrial applicability, as outlined above.